Fabrication of viscose



' fined herein as artificial fibers.

Patented Sept. 13, 1932 UNITED s'mxrus WILLIAM F. RICHTER, APOLLO, PENNSYLVANIA, AS SIGNOR T0 CHEMICAL HOLDING l CORPORATION, OF APOLLO, PENNSYLVANIA, A CORPORATION OF DELAWARE FABRICATION or vIscosE No Drawing.

This invention relates to the fabrication of viscose into useful products, especially to the production of artificial silk. 7

The precipitating baths used'commonly at the present time for viscose contain relatively large amounts of sulfuric acid, for example 8'per cent or more, together with rather high concentrations of one or more salts, such as sodium or magnesium sulfates. Such baths, which characterize commercial practice prior to my invention, are open to certain objections. For example, as a result of therather high concentrations of salts used, the yarn leaving the bath carries away relatively large amountsof salts, so that the baths become depleted quickly, which necessitates renewal of their salt components. Furthermore, the salts usually used tend to crystallize readily, and thus the yarn may become encrusted with them prior to washing. In consequence, not only must the yarn be subjected to prolonged washing, but also the removal of the crystallized material from its fibers may weaken the resultant product.

The objects of this invention are to provide an improved process of precipitating viscose, in which use is made of baths having not only a lower concentration of acid than those used heretofore, but also of salts, and having substituted for the salts now used others better suited for this purpose, whereby crystallization of salts upon the yarn is minimized and there is less danger of weakening of the thread during and after precipitation, and less frequent renewal of salts is necessary.

I have found, and it is upon this that the invention is predicated, that particularly favorable results are obtained in the fabrication of viscose through the use of a precipitating or spinning bath containing sulfuric acid, bismuth sulfate, and zinc sulfate. The invention is applicable to the fabrication of viscose into the various products which are made therefrom, all such products being de- In the use of baths containing sulfates of bismuth and zinc, lower concentrations of acid may be used than have heretoforebeen applied commercially, the exact concentration depending upon the product desired. In general it is Application filed October 7, I930. Serial No. 487,026.

preferred tohave thebismuth sulfate present in an amount in excess of the zinc sulfate.

The invention is especially applicable to the production of artificial silk. In this embodiment the bath most suitably contains from about 5 to 7 percent ofsulfuric acid, from about 1 to 3 percent of bismuth sulfate, and from about 0.5 to 2 per cent of zinc sulfate. The proportions here given refer to the anhydrous salts. My tests have shown that particularly suitable results are obtained with a bath of the following composition:

Sulfuric acid 6% Bismuth sulfate 2% Zinc sulfate 1% The bath is preferably used at an elevated temperature, for example between to 50 (3., and most suitably between 40 and C. As thus used, the practice of the invention provides lustrous silk of high quality.

Through the use of these bismuth sulfatezinc sulfate baths the salts are not removed as rapidly by the yarn as has been the case with prior baths, and therefore less frequent renewal of the salts, or replacement of the baths, is necessary. Furthermore, the salts used in the practice of the invention do not possess the strong tendency toward crystallization that is possessed by sodium and magnesium sulfates, and the others which have been commonly used, so that there is less tendency for them to crystallize in the yarn. Because of this, and because the yarn carries out so small an amount of salts, weakening of the yarn through crystallization and washing out of salts is minimized or eliminated. Otheradvantages, such as reduction in the amount of wash water needed, also attend the invention.

According to the provisions of the patent statutes, I have explained the principle and I claim:

1. In a process of preparing artificial fibers from viscose the step comprising precipitating the viscose in a bath containing from 5 about 5 to 7 per cent of sulfuric acid, about 1 to 3 per cent of bismuth sulfategand about 0.5 to 2.0 percent of zinc sulfate. 7 V

2. In a process of producing artificial silk from viscose the step comprising precipitatingth'e viscose in a bath containing from about 5Vto 7 per cent of sulfuric acid,- bismuth sulfate, and zinc sulfate in an amount less than said bismuth sulfate.

3. In a process of preparing artificial fibers from viscose the step comprising precipitating the viscose in a bathcontaining sulfuric acid in an amount sufiicient to coagulate the viscose but not exceeding about 8 per cent, and. also containing bismuth sulfate and zinc sulfate.-

In testimony whereof, I sign my name.

WILLIAM F. RICHTER. 

